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The assumption by counterterror police – who have led on this since the Salisbury attacks – is that if it can happen to the Skripals and Glushkov, it can happen to any of them

Senior source

Sources say the aim is to establish their “mood” and the private security measures put in place.

In two cases, officers followed up interviews with visits to oligarchs’ homes.

“The assumption by counterterror police – who have led on this since the Salisbury attacks – is that if it can happen to the Skripals and Glushkov, it can happen to any of them,” said a senior source.

“So the idea was to reach out to reasonably prominent members of the Russian diaspora in London critical of Putin, to speak about their safety and fears.”

One Russian who spoke to police was described as a wealthy former investment banker who fled to the UK in 2014 after criticising the Putin regime.

Another was a billionaire dissident who has been in London since the early 2000s.

The source said: “They responded to invitations to attend Kensington and Chelsea police station, where they were asked to characterise what their feeling was in terms of a heightened threat scenario, outline their private security arrangements and whether these were being increased.”

There are more than 150,000 Russians living in London, many of them pro-Putin.

The source said: “The individuals who have already spoken with police have been asked to speak to fellow members of the community.

Of course, it will be infiltrated with informants. The idea is that news of this operation gets back to Moscow.”

Following Mr Glushkov’s death, the Government said it would investigate the alleged links between Russia and 14 other deaths on UK soil in the past two decades.

Mr Glushkov, who was given political asylum in 2006, was a close friend of Putin critic Boris Berezovsky, found dead in his London home in 2013.

The Russian embassy “hit list” also allegedly includes billionaire banker Andrey Borodin, who fled to Britain just before he was due to be arrested for alleged fraud.

MI5 warned him in 2012 of “credible threats” against his life, involving a Chechnya hitman who had been offered $1million to kill him.